This invention relates to a method of fracturing and heating a gas hydrate formation to convert the hydrate into producible gas. In one aspect, the invention relates to a method of treating a subterranean formation underlying or within the permafrost.
The term "permafrost" refers to permanently frozen subsoil continuous in underlying polar regions and occurring locally in perennially frigid areas. Permafrost begins from a few inches to several feet below the surface and may extend downward as much as 1000 to 2000 feet, depending on its geographic location. In addition to granular ice in the interstices of the soil particles, there may be sizable bodies of solid ice.
In many areas, gas-bearing formations are found in close proximity to the base of the permafrost or within the permafrost itself. The proximity of the permafrost to gas formations has two significant effects: (1) the low temperature and pressure conditions of the gas in the presence of water results in a condition wherein the gas is trapped in a crystalline water structure in the form of a solid hydrate and (2) the low overburden pressure through the permafrost produces earth stresses such that fracturing treatments in or near the permafrost results in horizontal fractures.
The structure of the gas hydrate prevents removal of the gas from the formation by conventional production techniques. The application of heat, as by the injection of hot liquids, will cause the hydrate to dissociate and permit the release of gas, but the heat dissipates rapidly.
Hydraulic fracturing is a common technique of stimulating production by injecting a fluid into the formation at pressures and rates to cause the formation to fail and produce a fracture or crack therein. It is obvious that this technique is not applicable in gas hydrate formations because the hydrate remains immobile.
U.S. Pat. No. 5,620,049 discloses a well treatment process which combines hydraulic fracturing followed by heating the fracture using electric current. This process is disclosed in connection with the treatment of petroleum bearing formations, and not gas hydrate formations. The fracture generated in the subterranean formations disclosed in U.S. Pat. No. 5,620,049 is a vertical fracture. As described in more detail below, the method of the present invention requires that the fracture treatment produce horizontal fractures.